Motor-controlling system.



W. D. LUTZ.

MOTOR CONTROLLING SYSTEM.

APPLICATION FILED D110. 6, 1909.

Patented May 5, 1914.

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W. D. LUTZ.

MOTOR CONTROLLING SYSTEM.

APPLICATION FILED DEC. 6, 1909.

1,095,507. Patented May 5, 1914.

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MOTOR CONTROLLING SYSTEM.

1;O95,507. Patented May 5, 1914.

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Cay wanton UNITED STATES" PATENT OFFlGE.

WILLIAM D. LUTZ, OF ALLEN DALE. NEW 'J'EFSEY, ASSIGNOR TO OTIS ELEVATORCOMPANY, OF JERSEY CITY, NEW JERSEY, A CORPORATION OF NEW JERSEY.

MOTORFCONTROLIZING SYSTEM.

Specification of Letters Patent.

Application filed December 6, 1908.

Patented May 5, 1914.

Serial No. 531,496.

To all *uihomc't may concern Be it known that I, WILLIAM D. LU'rz, acitizen of the United States, residing in the borough of Allendale, inthe county of Bergen and State of New Jersey, have invented a new anduseful Improvement in Motor- Controlling Systems, of which the followingis a specification.

My invention relates to improvements in motor controlling systems andone of its objects is to improve upon the systems now in use and toprovide simple and efficient means for accomplishing this end.

A further object is the provision of means for effecting a dynamic brakeaction of the motor upon slowing down or stopping, and of automaticallyvarying the degree of said brake action.

Other objects will appear hereinafter, the novel combinations ofelements being pointed out in the appended claims.

My invention is particularly adapted to the cont-r01 of an electricmotor used for elevator service, wherein the motor, in slowing down orstopping, generates a current which is usedto effect a dynamic brakeaction of the motor, tending to reduce the speed of the same. Thisdynamic brake ac tion is all that is necessary to eflI'ect the desiredspeed reduction, although when it is desired to bring the motor to acomplete A stop, the retarding effect due to the dynamic brake action isaugmented by the use of the usual's'pring pressed friction brake.- Inele- Vat-or practice it is custo mary to arrange the motor controllingsystem in such. manner that as the car approaches either limit oftravel, the motor is automatically, gradually slowed down prior tostopping, by means of the dynamic brake action of the motor. In suchcases the retarding force of the dynamic brake action is so adjusted orproportioned that the rate of speed reduction will be best suited tomeet any particular condition met in' practice. It is found, however,that where the arrangement is such as to produce aproper speed reductionat the limits of travel, the stop produced by the operator in the car,should he suddenly move the controlling switch to stop position with themotor running at substantially full speed, is much too quick. This quickstop causes sparking at the brushes of the motor and imposes a severestrain upon the hoistmg mechanism, and, in the case of a direct drive ortraction elevator system, causes the cables to slip about the drivingsheath.

My invention is for the express purpose of so controlling or regulatingthe retarding effect of the dynamic brake action that an elevator carmay be brought to rest automatically at any point in its travel,smoothly and quickly without producing any jar or undue strain upon theelevator mechanism.

Figure 1 of the drawing represents diagrammatically a controlling systemfor an electric elevator embodying my invention. Fig. 2 shows insectional elevation, the detail construction of the electro-magneticswitch E of Fig. 1. Figs. 3, 4, 5, 6, 7, 8 and 9 illustratediagrammatically the constructions of the main, auxiliary and by-passresistances with respect to the motor armature for different posit-ionsof the operating or controlling switch S in the car.

Like characters of reference denote similar parts through all thefigures.

Referring tothe drawing, R and R designate mot-or starting and reversingswitches, while M is the armature of an electric motor.

F designates the motor field, and in the present instance is shown as asimple shunt winding, although my invention is not limited to shuntwound motors or motors of any particular type or winding.

I designates an auxiliary resistance which is used in starting orstopping the motor,

while H is the main starting resistance which is included in thearmature circuit of the motor upon starting and is automatically removedfrom, or out out of said circuit as the motor attains full speed. Theautomatic means for controlling the starting resistance H consists of anaccelerating magnet A. which effects the closure of a plurality ofcontacts, 34, 35, 36 and 37 in successive order or sequence, thesecontacts being connected to the resistance at suitable point-s thereon.

B designates the magnet winding of the usual spring pressed electricallyreleased brake apparatus which operates to retard the rotation of abrake or friction pulley secured to the armature shaft. The brake are intheir raised position.

mechanism is not illustrated herewith since it involves nothing new andis widely used, hence a detail description is not considered necessary.

C designates a suspended elevator car which may be operatively connectedto the motor armature M after the usual manner.

S is a hand switch in the car, by means of which the motor may bestarted, stopped and reversed in a manner to be pointed out hereinafter.

J designates a bypass resistance while I), E and Gr are electro-magneticswitches for controlling certain circuits used in connection with myinvention.

Having given a brief description of the various parts used in carryingout my invention, I will now describe in detail certain of the moreimportant parts, at the same time tracing the circuits associatedtherewith so that a clear understanding may be had of the operation ofthe system as a whole.

The reversing switches R and R are similar in construction and eachcomprises a solenoid core 7 to which is connected a rod 6. Fastened tothis rod 6 are two insulated pieces 4.- and 5 to which are securedcontacts 11, 11, 13 and 16, 141 respectively. Directly below thecontacts 16 and 14 are stationary contacts 17 and 15 respectively whichare normally in contact therewith. Other stationary contacts 10 and 12are located directly above the contacts 11, 11 and 13 respectively andunder certain conditions are placed in electrical engagement therewith,that is, when the core 7 and connected parts Surrounding the core 7 aretwo magnet windings S and 9, the winding 8 being adapted to raise thecore 7 and connected parts when energized, while the winding 9 undercertain conditions tends to pull the core 7 downwardly.

In order to start the motor to raise or lower the elevator car C, theoperator effects the energization of one or the other of the reversingswitches R and R by moving the lever 53 of the ear switch S to the leftor right. We will assume that this lever is moved to the left until itassumes the position indicated by the broken line 1. In this positionthe lever 53 is in electrical engagement with the stationary contact 54,thereby establishing a circuit to the magnet winding 8 of the reversingswitch R. This circuit may be traced as follows: from the main by wire61, to and through the winding 8, Wire 58, contact 54, switch lever 53,and'by wire 57 to the main. The Winding 8 is thereby energized to raisethe core 7 and connected parts, thus causing the contacts 11, 11 and 13to engage the contacts 10 and 12 respectively and at substantially thesame time, separating the contacts 16, 17 and 14c, 15 respectively. Thisoperation closes a circuit to the motor armature and brake magnet, andat the same time short circuits the resistance L which heretofore was inseries with the motor field. The brake magnet circuit is closed at thecontacts 12 and 13 and the friction brake is thus released, allowing themotor to rotate freely. The armature circuit may be traced as follows:from the main by way of the contacts 10 and 11, wire 18, contacts 19and 20 of the reversing switch R, wire 30, magnet windings 9 and 9, wire29 to the brush 28, through the motor arma- .ture M, brush 27, wire 26,contacts 24 and 23 of switch E, wire 22, portion a of the auxiliaryresistance I, wire 21, contacts 32 and 33, wire 31, and through the mainresistance H to the line. The motor now receives current and starts torotate at slow speed with full field strength, the current passingthrough the motor armature being limited in amount by reason of theresistance in series therewith and also by reason of the bypassconnection around, or in shunt to, the motor armature. This by-passcircuit comprises the portion 0 of the bypass rcsistance J and may betraced from the armature brush 28, wire 29, magnet windings 9 and 9,wire 61, resistance a, contacts 41, wires 40 and 26 to the motor brush27. It will be noticed that portion (Z of the bypass resistance J andthe portion 1) of the auxiliary resistance I are not in circuit at thistime since they are short-circuitcd by the contacts 44, 42, 41 and 23,24; respectively. The electromagnets A, G and D will not operate at thistime since their circuits are open. The electromagnet I) will alsoremain inoperative as it is connected directly across the arn'laturebrushes, and, as the potential across the brushes at this time is of lowvalue, the magnet E will not receive sufiicient current to raise itsmagnet core 50 and connected contact plate 25. The above condition ofcircuits is represented diagrammatically in Fig. 3, the lever of the carswitch being in position designated by the broken line 1 in Fig. 1.

In order to increase the speed of the motor, the car switch lever 53 isadvanced until it assumes the broken line position 2, in which itengages both of the stationary contacts 5 1' and 55. This movementcloses a circuit to the electromagnet D, this circuit being traced fromthe main by way of the contacts 10 and 11, wires 18 and 65, magnetwinding 52, wire 59, contact 55, switch lever 53, and by wire 57 to theline. The winding 52 of magnet D is thereby energized to raise its core51 and connected parts, thus separating the contacts 41 and placing thecontacts 39 in electrical engagement with each other. The separating ofthe contacts 41 efiects the removal of the short-circuit around theportion (1 of the entire resistance J in shunt to, or across, the

. motor brushes.

This by-pass circuit may now be traced from the brush 28, wire 29,magnet windings 9 and 9, wire 64, resistance J, contacts 42 and 44, andby the wires 45 and 26 to the brush 27. Since the contacts 39 areconnected to opposite ends of the resistance I, the closing of thesecontacts by the energization of the winding 52 of switch D shortcircuits the entire resisttime I. The motor now accelerates in speed forthe reason that the portion a of the auxiliary resistance which wasformerly in se ries with the motor armature has been shortcircuited andalso because the by-pass resistance across the motor brushes has beenincreased by the addition of the portion d. It should be observed thatany operation of the magnet switch E at this time will produce no effectwhatsoever, since the entire resistance I is short-circuited by thecontacts 39 of switch D, hence the opening or the contacts 24, 23 willnot affect the resistance I in any way. The condition of the motorcircuits as they now stand is shown in Fig. 4.

In order to bring the motor to full speed, the car switch lever 53 isfurther advanced into the position indicated by the broken line 3,wherein the lever 53 is in electrical engagement with the contacts 54,55 and 56. This operation closes a circuit to the magnet switch Gr, thiscircuit being traced as follows :frpm the line by way of the contacts 10and 11, wires 18 and 65, magnet winding 47 of switch G, wire 60, contact56, switch lever 53, and by wire 57 to the main. The energization of thewinding 47 causes the core 46 to move upwardly, thereby open circuitingthe contacts 42 and 44 by removing the bridging member 43 out ofengagement therewith, and also effecting an electrical engagement of thecontacts 48. Upon open-circuiting the contacts 42 and 44 the by-passresistance J is open-circuited, while the closing of the contacts 48establishes a circuit to the magnet-winding of the accelerating magnetA. By tracing the circuit of the accelerating magnet A, it will be seenthat its terminals are connected across a circuit comprising the motorarmature and a small portion of the main starting resistance H, thus thewinding of this magnet will be subjected to the counter-electro-motiveforce of the rotating armature. As the motor accelerates in speed themagnet A will automatically operate successively to close the contacts34, 36 and 37 controlled thereby in successive order and in this mannerthe starting resistance II will be short-circuitcd step-by-step and themotor will gradually attain full running speed, its armature beingconnected directly across the mains. This condition of circuits is shownin Fig. 5. If the operator in the car had moved the switch lever 53 tothe right, the operation would have been similar to that just pointedout excepting that the magnet 8 would have been energized instead ofthemagnet 8, and the reversing switch R controlled thereby would close thecircuits in such a way as to cause the motor armature to rotate in theopposite direction.

The operation of stopping may be effected by moving the lever of the carswitch slowly back to its center or off position, or by placing the carswitch lever full speed position andallowing the automatic switches atthe top and, bottom limits, to operate, or the car switch may besuddenly moved to off position to effect a more rapid stop. In order tostop the motor slowly, the operator moves the lever of the car switchback until it reaches the position indicated by the bro-ken line 2, orout of electrical engagement with the contact 56. The circuit to thewinding of magnet switch G is now interrupted and the core 46 drops,thereby open-circuiting the contacts 48 and again placing the contacts42 and 44 into electrical engagement. The separation of the contacts 48open-circuits the winding of the accelerating magnet A, and the mainstarting resistance H is again placed in series with the motor armatureacross the line. The bridging of the contacts 42 and 44 re-inserts theby-pass resistance J across the motor brushes. It is seen that thereinsertion of the resistance H in the armature circuit will, undercertain conditions. reduce the armature current and speed, while theplacing of the resistance J in shunt to the armature will effect. areducwinding 52 of switch I) at the switch contact 55. The switch Dimmediately drops its contacts; the lower ones, 41, short-circuiting theportion d of the bypass resistance, thereby lowering the resistanceacross the motor brushes and increasing the dynamic brake effect, whilethe upper contacts 39 become separated and open the short circuit aroundthe resistance I and placing the phrtion a of the auxiliary resistanceback in series with the motor armature and the main resistance H. Theeffect of this operation is to further reduce the speed of the-motor andto reduce the amount of current flowing to the motor from the main linewhich effects a substantial economy in current consumption. The magnet Ein the meanwhile will have become deenergized, an amount sufficient nolonger to retain its core in "raised position, owing to the reducedspeedffof the motor and subsequent low counter jeh'zctromotive-force ofthe armature, hence the same drops its core and electrically connectsthe contacts 23 and 24, thereby sh0rt-circuiting the portion 6 of theauxiliary resistance I. The motor circuits under the above conditionsare shown in Fig. 3. If the load on the motor at this time is such as toexert a strong driving force, the electro-motive force will remain highenough to maintain the magnet of switch E energized so .that thecontacts controlled thereby are not in electrical engagement. In. thiscase the portion 6 of the resistance I will not be shortcircuited untilthe electro-motive-force and speed of the motor are reduced suilicientlyto permit the magnet E to drop its contacts. This condition of motorcircuits would be represented by Fig. 7. The car switch is next broughtto center or oif position, thereby open-circuiting the winding 8 of thereversing switch R and causing the contacts 14, 15 and 16, 17respectively to come into electrical engagement, and at substantiallythe same time interrupting all current from the main line at thecontacts 10 and 12. The drop-ping of the reversing switch R establishesa second dynamic brake circuit including the portion a of the auxiliaryresistance I, this circuit being traced as follows :from the brush 28,through the winding 9 and 9, wire 3O, contacts 20 and 1.9 of reversingswitch R, wire 18, contacts 14 and 15 of reversing switch R, wire 21,portion a of the resistance I, wire 22, contacts 23 and 24, and by wire26 to the opposite brush 27. The dynamic brake eifect is thereforegreatly increased since the current generated by the motor running as adynamo, is short-circuited through a comparatively low resistance. Thispowerful dynamic brake action is assisted by the friction brake whichcomes into action at this time since the circuit to its magnet winding Bwas open-circuited at the moment the reversing switch R dropped itscontacts. In this manner the motor comes to rest, the condition of itscircuits at this time being shown in, Fig. 9.

Should the motor be running at substantially full speed and developing acorrespondingly high counter-electro-motiveforce, and the gar switchlever be rapidly brought back to its center or stop position, it isreadily seen that the dynamic brake action would be too powerful, owingto the high speed of the motor, hence it becomes necessary or desirableto reduce or render less powerful the dynamic brake action at this time,and this I most effectually accomplish by means of the switch E. Asbefore pointed out, the magnet 49 of switch E is connected directlyacross the brushes of the motor, hence it will depend for its operationupon the electromotive-force of the armature. When the operator moveshis switch lever rapidly from full speed position to stop position, themagnet 49 is excited with maximum current, hence the core 50 will be inraised position, and the portion Z) of the auxiliary resistance I is notshortcircuited by the contacts 23 and 2 1. Thus it is seen that thedynamic brake circuit established by the deenergization of the reversingswitch magnet 8, now includes the whole of the auxiliary resistance Iinstead of only the portion a, and, since the resistance of this circuitis greater than the resistance of the circuit which includes only theportion a, it follows that the current flow, as well as the dynamicbrake action, are substantially reduced. This condition of motorcircuits is represented by Fig. 8. As the motor slows down, itselectro-motive force is reduced until finally the magnet 49 is no longerable to sustain its core in raised position, hence the latter will dropand place the contacts 2s and 23 into electrical engagement with eachother. This operation increases the dynamic brake action byshort-circuiting the portion 6 of the resistance I and allowing morecurrent to flow. In this manner the magnetic switch E automaticallycontrols the dynamic brake action by the varying electro-motive-force ofthe armature. If so desired, the magnet E may be a multiple magnet, or aseries of magnets whose contacts may be connected to intermediate pointsalong the resistance I so as to insert or cut out of circuit portions ofthis resistance, and in this manner graduate the steps of resistance,thus tending to produce a smoother stopping effect and greaterrefinement in operation. hen it is desired to employ more than a singlemagnet switch E to insert or cut out of'circuit the resistance I insteps, I prefer to arrange a series of magnets so that they will operatein a certain definite order or sequence, not only when these magnetsrespond to an increase in potential of the motor armature, but also whenthey respond to a drop in potential. This feature may be attained bymeans of the construction shown in- Fig. 2 or in other ways well knownin the art.

Referring to Fig. 2, it is seen that the magnetic switch E comprises aniron-clad magnet having a frame 68 which incloses the winding 49 andprotects it against mechanical injury. The winding 49 is wound upon aninsulated spool 7 2 through the center of which passes a brass tube 73.The magnet core 50 is arranged to slide freely in said tube, at theupper end of which is arranged an adjustable plug 69 of iron or othermagnetic material. This plug may be raised or lowered in the tube 73 soas to vary the air gap between the core 50 and 50 limits-the movement ofthe latter in an upward direction. The shoulder 70 is threaded upon themagnet stem 76 and may be secured in any desired position thereon bymeans of the lock nut 75. 74 is a washer of leather or other'resilientmaterial which engages the lower face of the magnet frame 68 when thecore 50 is in its raised position and thus eliminates all slamming andnoise which would be occasioned were not some such means provided.

A switch constructed in the above manner may be arranged to both raiseand drop its core at any desired time by varyin the position of the plug69 and shoulder 0.

I am aware that-it is not broadly new to place a resistance across themotor brushes in stopping in order that the current generated by themotor running as a dynamo may be absorbed and so effect a retardation ofthe motor armature, but I believe it to be new in the art to control theamount of this resistance according to the varying potential of thearmature. It is evident that the amount of resistance which is placed inshunt to the armature at the moment of stopping when the armature isrotating at high speed, should beat a maximum because at such time theelectro-motive-force is at its highest point. Furthermore it isdesirable to reduce the amount of this resistance as the motor slowsdown and its electro-motive-force decreases so that the dynamic brakeaction may be maintained sufiiciently powerful to act effectively aslong as the motor armature continues to rotate. By

; means of my invention the dynamic brake action applied to stopthe-motor when the so that the braking effect tending to retard themotor armature increases as the same undergoes a reductlon 1n speed.This feature is of great practical value, as I have found by actualexperience that the motor, even under heavy loads and traveling at highrates of speed and used with such connections, as with elevators, can bequickly and easily stopped without producing ars or jolts, and the mostexacting requirements in connection with this class of work can bereadily fulfilled.

It will be seen that the deenergization of the reversing switch ma et 8does not opencircuit the shunt field winding F but merely introduces aresistance L in series therewith. In this manner the field is kept aliveso as to be sure that the rotating armature will generate a current whenthe reversing switches are in open position, and not relying upon thesmall residual field left in the motor after opening the shunt fieldcircuit.

While this arrangement is desirable, it is not essential.

Referring again. to Fig. 1, it will be seen that all current passingthrough or generated by the motor armature also passes through bothwindings 9 and 9. These windings are arranged to produce a downward pullupon their respective cores 7 and 7 when the latter are in theirlowermost positions. The function of these magnets is of considerableimportance since it prevents the operator in thecar from suddenlyreversing the motor. The reason for this is due to the fact that as soonas the operator attempts to' suddenly reverse, a dynamic brake circuitis established through the windings 9 and 9' and the downward pull thusholds both reversing switches in their lowermost position against anytendency of the magnets 8 or 8 to raise or close these switches untilthe dynamic brake current generated by themotor in the windings 9 and 9has been greatly reduced, which current reductiouis proportional to thereduction in speed of the rotating armature. This feature for preventinga too sudden reversal of an electric motor is described at length andthe novel features thereof claimed in my co-pending application filedNovember 22nd, 1909 Serial No. 529,221.

I desire not to be limited to the precise construction and arrangementof parts herein disclosed, since it is obvious that those skilled in theart could readily make various changes in the details thereof withoutdeparting from the spirit and scope of my invention.

What I claim as new and desire to have protected by Letters Patent ofthe United States, is

1. In a system ofmotor control, the combination with a motor, ofcircuits therefor including parallel circuits to the armature, aresistance in one of said parallel circuits, and automatically operatedmeans dependent on the speed of the motor for varying said resistance inresponse to reduction in the motor speed while the other circuit isclosed.

2. In a system of motor control, the combination with a motor, of. meansfor connect- 1 nesting and disconnecting the motor to and I from asource of current supply, circuits for the motor including a parallelcircuit to the armature, a resistance in said parallel circuit, andelectromagnetic means for varying said resistance according to thevarying potential of the motor armature while the motor is disconnectedfrom said source of. supply.

4:. In a system of motor control, the combination with a motor, of meansto connect the motor to current supply means,- circuits for the motorincluding a parallel circuit to the armature, resistance in saidparallel circuit, electromagnetic means for varying said resistanceaccording to the varying potential of the motor armature while the motoris disconnected from the supply mains, and means for controlling theoperation of said electromagnetic means. i

5. In a system of motor control, the combination with a motor, ofcircuits therefor including a resistance, means for connecting saidresistance in series with the motor armature upon starting, and for.connecting said resistance in parallel to the motor armature uponstopping, and means operated by the motor for varying said resistance inresponse to variations in the speed of the motor armature.

6. In a system of motor control, the combination with a motor, ofcircuits therefor including aresistance, an electro-responsive devicefor connecting said resistance in series and parallel relation to themotor armature, and means operated by the motor for varying saidresistance when in parallel relation in response to the varyingpotential of the motor armature.

7. In a system of motor control, the combination with a motor, ofcircuits therefor including a resistance, an electro-responsive devicearranged to connect said resistance in series or parallel relation tothe motor armature, and means operated by the motor for varying saidresistance when the latter is in parallel relation.

8. In a system of motor control, the combination of a motor, a source ofelectrical supply, a resistance, an electro-responsive device adaptedwhen in one position to connect the motor and resistance to the sourceof electrical supply, and when in another position to disconnect saidsource of electrical supply, and connect the motor and resistance inparallel to each other, and means effected by the varying potential ofthe motor, armature for controlling said resistance.

9. In a system of motor control, the combination with a motor, of meansfor closing a parallel circuit to the motor, additional means forclosing a second parallel circuit to the motor and maintaining both ofsaid circuits closed at the same time, resistance in both of saidparallel circuits, and means dependent upon the motor for varying theresistance in one of said parallel circuits.

10. In a system of motor control, the combination with a motor, of meansfor effecting a decrease in speed of the same, said means comprising aresistance connected in parallel to the motor armature, an additionalparallel circuit to the motor armature containing resistance foreffecting a further speed reduction, and means for varying said lastnamed resistance.

11. In a system of motor control, the combination with a motor, of acircuit containing resistance in parallel relation to the ar mature ofsaid motor, an additional circuit containing resistance in parallel tothe motor armature, and means operated by the varying potential of themotor armature for varying the resistance in one of said parallelcircuits while the other circuit is established.

12. In a motor control system, the combination with a motor, of aplurality of par allel circuits to the armature of said motor,resistance in each of said circuits, means for closing said circuits,and means dependent upon the speed of the motor for effecting avariation of the resistance in one of said parallel circuits while bothof said circuits are closed.

13. In a motor control system, the combination with a motor, of twoindependent circuits containing resistance arranged to be connected inparallel to the motor armature, electromagnetic means for closing saidparallel circuits, and means automatically operated according to thevarying potential of the motor armature for controlling the resistanceof one of said independent circuits while the other circuit is closed.

14. In a motor control system, the combination with a motor, of aplurality of circuits containing resistance arranged in parallel to themotor armature and to each other, means for controlling said circuits,electromagnetic means controlled by the motor for varying the resistanceof one of said circuits, and means for regulating the operation of saidelectromagnetic means.

15. In a system of motor control, the combination with an electricmotor, of a plurality of circuits each containing resistance, means forconnecting one or more of said circuits in parallel to the motorarmature, and an electromagnet automatically operated according to thevarying potential of the motor armature for controlling the re sistancein one of said circuits while the other of said circuits is established.

16. In a system of motor control, the combination with an electricmotor, of a plurality of circuits each containing resistance, means forconnecting said circuits in parallel to the motor armature, anelectromagnet controlled by the speed of the motor and arranged tocontrol the resistance in one of said parallel circuits while theresistance of the other circuit is in parallel with the motor, and meansfor controlling the operation of said electromagnet.

17. The combination with a motor, of a resistance, means for connectingsaid resist ance in series and in parallel to the motor armature, andmeans operated by current from the motor for varying said resistance inresponse to variations in the motor speed when the resistance is inparallel relation with respect to the motor armature.

18. The combination. with an electric motor, of a resistance connectedin series therewith, an additional resistance connected in parallel tothe motor armature, electro-magnetic means arranged to connect saidfirst named resistance in parallel to the motor armature to reduce thespeed of the same, and means controlled by the motor for varying theresistance in one of said parallel circults.

19. The combination with an electric motor, of a resistance connected inseries therewith, an additional resistance connected in parallel to themotor armature, electromagnetic means for simultaneously varying both ofsaid resistances to increase the speed of the motor, means forconnecting said first named resistance in parallel to the motor armature to reduce the speed of the latter, and means controlled by thevarying potential of the motor armature for varying the resist ance inone of the parallel circuits to the motor armature.

In testimony whereof, I have signed my name to this specification in thepresence of two subscribing Witnesses.

WILLIAM D. LUTZ. lVitnesses:

JOHN F. Roms, AUGUST SUNDH.

